As DRAMs increase in memory cell density, there is a continuing challenge to maintain sufficiently high storage capacitance despite decreasing cell area. Additionally, there is a continuing goal to further decrease cell area. One principal way of increasing cell capacitance is through cell structure techniques. Such techniques include three-dimensional cell capacitors, such as trenched or stacked capacitors. Yet as feature size continues to become smaller and smaller, development of improved materials for cell dielectrics as well as the cell structure are important. The feature size of 256 Mb DRAMs and beyond will be on the order of 0.25 micron or less, and conventional dielectrics such as SiO.sub.2 and Si.sub.3 N.sub.4 might not be suitable because of small dielectric constants.
Highly integrated memory devices, such as 256 Mbit DRAMs and beyond, are expected to require a very thin dielectric film for the 3-dimensional capacitor of cylindrically stacked or trench structures. To meet this requirement, the capacitor dielectric film thickness will be below 2.5 nm of SiO.sub.2 equivalent thickness. Insulating inorganic metal oxide materials have high dielectric constants and low leakage current which make them attractive as cell dielectric materials for high density DRAMs and non-volatile memories. Most all of these materials incorporate oxygen and are otherwise exposed to oxygen and anneal for densification to produce the desired capacitor dielectric layer.
In many such applications, it will be desirable to utilize conductive metal oxides as the principal material for one or both of the conductive capacitor electrodes. Conductive contact to the outer, or cell, electrode layer in DRAM circuitry is typically made through a contact opening formed within an electrically insulative material. The opening is subsequently filled with one or more conductive materials, such as titanium, titanium nitride and/or tungsten, to form the conductive contact to the cell electrode. Unfortunately, these materials are capable of oxidizing to a non-conducting metal oxide upon effective exposure to the overlying conductive metal oxide. For example, exposure to temperature as low as 200.degree. C. can cause oxygen from the conductive metal oxide to react with one or more of titanium, titanium nitride and tungsten to form an insulative oxide, and effectively block the electrical connection.
Overcoming such problem in DRAM circuitry fabrication was a motivation for the invention, but the invention is in no way so limited.